1. Field of the Invention
This invention relates to a block-type dielectric filter, and a dielectric duplexer which includes the dielectric filter, and a communication apparatus which includes the filter and/or the duplexer.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 5-183309 (No. 1) discloses a dielectric resonator device comprising an inner-conductor-coated hole disposed in a dielectric block having substantially a rectangular solid shape, wherein part of the inner-conductor-coated hole is an inner-conductorless portion. The inner-conductorless portion forms an open-circuited end of a resonator. Further, Japanese Unexamined Utility Model Publication No. 63-181002 (No. 2), discloses a dielectric resonator device in which the outer-conductor on one end surface of a dielectric block is eliminated so that said end surface is made an open (open-circuited) end surface.
In a dielectric filter having the structure of No. 1, because the open end of a resonator is located below the outer-conductor on the outer surface of the dielectric block, leakage of the electromagnetic field and higher-order spurious radiation are suppressed. Further, as the open end of the above resonator can be formed by cutting the inner-conductor inside the inner-conductor-coated hole, the dielectric filter has the advantage that the adjustment (fine adjustment) of each of the resonators is made possible.
Further, in a dielectric filter having the structure of No. 2, the capacitance between the input-output electrode and the outer-conductor (earth) becomes relatively smaller compared with the structure of No. 1, when an input-output electrode is disposed around the open end surface of the dielectric block and the input-output electrode and inner-conductor are capacitance-coupled. Thus, the input-output electrode can be reduced in size and the degradation of the no-load Q (Q0) of the resonator can be prevented. Further, when the open end surface is formed, because the open end surface of a plurality of resonators can be formed collectively in a single manufacturing step, the manufacturing cost is kept down.
However, in the dielectric filter having the structure of No. 1, because the capacitance between the input-output electrode and the outer-conductor (earth) becomes large, the area of the input-output electrode cannot help but be increased in order to realize sufficient coupling to the resonator. As a result, a large input-output electrode is given where originally an outer-conductor (earth) electrode was located. Therefore, the conductor loss of the resonator is increased and Q0 of the resonator is degraded. Further, because each of the resonators is constructed by a method wherein the conductor of each of the inner-conductor-coated holes is removed individually, the total number of manufacturing steps increases and the processing cost rises.
Further, in the dielectric filter having the structure of No. 2, because the open surface side is exposed to the outside, the electromagnetic field leaks in that portion and higher-order spurious radiation is likely to be emitted. Further, because the open surface is processed in a single step, the individual adjustment of each of the resonators becomes difficult.
To overcome the above described problems, embodiments of the present invention provide a dielectric filter and a dielectric duplexer which simultaneously have the advantages of the dielectric filters disclosed in the above No. 1 and No. 2, and a communication apparatus including the filter and duplexer.
One embodiment of the present invention provides a dielectric filter comprising: a dielectric block having a substantially rectangular solid shape; a plurality of inner-conductor-coated holes disposed inside the dielectric block; the end portion of at least one inner-conductor-coated hole being at an open surface of the dielectric block on which the outer-conductor is not disposed, an input-output electrode being capacitance-coupled to the vicinity of the end portion of the inner-conductor-coated hole; and both end portions of at least one inner-conductor-coated hole, other than the one that is capacitance-coupled to the input-output electrode, are connected to the outer-conductor, and an inner-conductorless portion is provided inside the hole.
According to the above described structure and arrangement, as the end portion of an inner-conductor capacitance-coupled to an input-output electrode is an open surface of the dielectric block, the required capacitance between the input-output electrode and outer-conductor decreases, the area of the input-output electrode becomes relatively small, and a sufficient predetermined capacitance can be maintained between the input-output electrode and the vicinity of the open end of the inner-conductor. Therefore, the Q0 of the resonator does not decrease. Further, regarding the inner-conductor-coated hole that is not capacitance-coupled to the input-output electrode, because both end portions are connected to the outer-conductor, the leakage of electromagnetic fields and higher-order spurious radiation are suppressed.
Accordingly, a dielectric filter having the characteristics of low insertion loss, low spurious radiation, and small leakage of electromagnetic fields is obtained.
In the above described dielectric filter, at least one of the two end portions of the at least one inner-conductor-coated hole which is not capacitance-coupled to the input-output electrode is arranged at a location sunken below the open surface.
According to the above described structure and arrangement, in the same way as the short-circuited surface, an outer-conductor is formed in a single step on a surface to be made an open surface, and the entire open surface can be formed at the same time by cutting the outer-conductor. In this step, however, the outer conductor on the short-circuited surface is not removed because it is sunken below the open surface. Accordingly, the manufacture of the dielectric filter becomes easy.
In another embodiment of dielectric filter according to the invention, at least one of the two end portions of the at least one inner-conductor-coated hole which is not capacitance-coupled to an input-output electrode is arranged on a plateau which protrudes above the open surface.
Generally, when an inner-conductorless portion is formed inside an inner-conductor-coated hole, the effective resonator length becomes shorter than the axial length of the inner-conductor-coated hole. But according to the above described structure and arrangement, the effective resonator length of a resonator made up of an inner-conductor-coated hole having an inner-conductorless portion can be made equivalent to the resonator length an inner-conductor-coated resonator which is capacitance-coupled to an input-output electrode. As a result, it is made easier to design a filter with predetermined characteristics.
Another embodiment of the present invention provides a dielectric duplexer comprising: a dielectric block having a substantially rectangular solid shape; a plurality of inner-conductor-coated holes disposed inside the dielectric block; the end portion of at least one inner-conductor-coated hole being at an open surface of the dielectric block on which the outer-conductor is not disposed, and at least one input-output electrode being capacitance-coupled to the vicinity of the end portion of the inner-conductor-coated hole; and both end portions of at least one inner-conductor-coated hole which is not capacitance-coupled to an input-output electrode are covered by the outer-conductor, and an inner-conductorless portion is provided inside the hole.
According to the above described structure and arrangement, a dielectric duplexer which can be used as an antenna-sharing device having the characteristics of low insertion loss, low spurious radiation, and small leakage of electromagnetic fields is obtained.
Yet another embodiment of the present invention provides a communication apparatus including the above described dielectric filter and/or dielectric duplexer in the high-frequency circuit portion thereof.
According to the above described structure and arrangement, a communication apparatus having a high-frequency circuit with low loss, low spurious radiation, and small leakage of electromagnetic fields is obtained.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.